It is known in the art that railway equipment must support and guide rail transit vehicles circulating through transportation networks. Insulating supports, known as “rail clamps”, are used in rail fastening systems to fasten rails to base slabs in public subways, for example.
Rail clamps are used to hold and anchor the rail to the reinforced concrete track. To be usable, rail clamps must show a high mechanical bending strength and also must allow the electrical insulation of the rail. Furthermore, when a train goes across the rail, the rail clamp must be somewhat bendable, i.e. it must produce movement so that the rail may slightly lift.
Due to the mechanical and dielectric requirements mentioned above, rail clamps have almost exclusively been made of steel and rubber. They are made of a metallic body partially covered with insulating rubber and optionally with lacquer. The rail clamp's steel is cast in foundries, the seams of the piece being created by the mold being removed by decoring or tumbling, or by another standard procedure. Steel often has a rigidity modulus of 10 to 20 million psi. The surface of the steel piece where the rubber must be placed is prepared according to specified procedures. Often a finish must be used before vulcanizing the rubber, to mold it on the metallic piece.
The process to manufacture rail clamps in two parts comprises many manufacturing, preparation and reinforcement steps, which increases the amount of time and production cost.
Furthermore, rail clamps made of steel and rubber are prone to rust, which leads to the separation and the eventual partial peeling between the components. Subways are often underground, which is usually a humid environment. Consequently, steel and rubber two-part rail clamps are very prone to rust. Rusting is especially fast in locations where surface tensions are the highest, i.e. the surface of contact between rubber and steel. Furthermore, when railway tracks are placed outdoors, they are exposed to rain, which can worsen rusting and lead to electrical leaks.
One major problem encountered with the use of this type of rail clamp made from materials combined into distinct layers is when rust has covered a certain amount of surface between the rubber and steel parts, the rubber peels away from the steel. This peeling can create a short-circuit. Known rail clamps comprise metallic parts which are conductive and which provide the structural mechanical properties of the rail clamp piece.
Rail clamps are often used in rail systems as shown in FIGS. 1 and 2. These Figures show a side of a track (1) with a rail (12). The rail clamps (10) are there to fasten the rail (12) to a base slab (14).
As illustrated, the rail clamp (10) is used to keep the rail (12) against an insulating rail road saddle (16) or directly against a rail road tie (14). Preferably, the rail (12) is placed in an insulating saddle (16). The rail clamps (10) are then placed as to overlap the part of the rail (12) in the insulating saddle (16) and the edge of the saddle. Advantageously, the rail clamps (10) hold the rail (12) to the saddle (16) by using a screw (18) that goes through the rail clamp (10) and the saddle (16). The screw (18) can be a bolt held down by a nut (15). The rail clamp (10) fastens the rail (12) in place like a clamp.
Other elements of the rail system are a carrying wheel (20); a guide wheel (24); a guide bar (26); insulators (28); and a running track (30) (made of steel as seen in FIG. 1 or of concrete as seen in FIG. 2).
FIG. 3 shows that the rail clamps can be spaced out to fasten the rail.
Another type of rail clamp used to fasten the rail to the base slab is a “hooked spike” rail clamp, which is made of two parts and which is part of the “hooked spike” railway system, as shown in FIG. 4.
The “hooked spike” system (32) comprises a “hooked spike” clamp (34) and a modified saddle (36) with a lower section (38) bearing a hole (40). The hooked spike rail clamp (34) effectively acts as a hook clamp element, and is usually shaped as a helical clamp comprising a first end, a second end and a leverage point between them. This first end is inserted in the hole (40) of the lower section, the second end (42) pushes against the rail while the leverage point pushes against the lower section (38), allowing the rail to be clamped to the base slab. FIG. 5 shows the modified saddle (36) used in this type of railway system.
The lower section (38) of the modified saddle (36) is usually made of an insulating material such as a polymer, while the hooked spike element (36) is often metallic. There is thus still a joint construction which can lead to rusting and separation problems. Furthermore, this hooked spike system comprises metallical elements that conduct electricity and/or joint components that lead to problems and difficulties in ensuring the safety of workers and the general public.
The hooked spike clamp system is costly and makes installation and inspection difficult.
FIG. 6 shows a railway system in which a rail clamp according to prior art is used. This rail clamp comprises a steel body (17), and a rubber sheet (19) at one end. FIG. 7 shows saddle with edges (42) which define a groove (44). Rubber can be put in the groove (44) to be in contact with the rail, optionally to reduce vibrations. This type of rail road saddle often needs to be manufactured by compression molding.
FIG. 8 shows a known rail clamp. This rail clamp (10) comprises a steel body (17) with a hole (45) and a rubber coating (19).
The current used in these systems is often from 748 to 778 Volts. It is very dangerous to work with these high voltages and monitoring of these rail clamps is very important, arduous and expensive.